HOW TO CHANGE THE GEARBOX OIL IN YOUR HARLEY DAVIDSON TWINCAM SOFTAIL.
Regular gearbox oil changes on your Hog will provide you with constant smooth shifting and long component life.
Changing the gearbox oil yourself is a really easy job you can do at home with a few basic tools. The service manual recommends changing the box oil every 5000 miles (8000 kms) but I halve the intervals on my personal bikes. Every 2500 miles on the dot. I've found halving the service schedule for fluid changes keeps the shift action smooth and clunk free.
You'll need some gearbox oil. The manual recommends 20 - 24oz (590 - 710ml) of HD gearbox lubricant. I've found that 650ml (22oz) fills the box to the proper level on my '05 Softail. You can actually use almost any automotive gear oil in the box but some viscosity weights will obviously work better than others.
A lot of people run an automotive multigrade heavy gear oil in their Harley gearboxes with great success and I'm one of them. I use an 85w - 140 grade performance gear oil in both my old Evo and my twincam and the damn things have never shifted better. Far better than the Harley oil or syn3 ever did.
You'll need a new gearbox drain plug O-ring from the stealership (only a few bucks).
The tools you need are:
A 3/8 inch drive socket set that has a 5/8 size socket, a ratchet, a uni-joint and extension bars. A 3/8 drive set will fit up between your shocks to get at the drain plug where a 1/2 inch drive set will not fit for love or money !
An imperial Allen key set with 3/8 and 7/32 sized keys.
Righto, time to get dirty.
Here is your gearbox fill plug that doubles as a dipstick. It is located on the same side as your pipes.
Its a bit easier to see in this shot.
To find the drain plug you're gonna have to get down and dirty !!
Nope... still can't see it from here. You're gonna have to get your noggin right under the bike !
Its in a prick of a spot hey ? Don't let it worry you though, getting it out with the right tools is a snack.
And this is what the right tools look like.
Here's a close up of the uni-joint ... life is easy when you've got one of these in the toolbox !!
Slap your 5/8 socket on the end and we are ready to rock.
First we need to get the filler plug / dipstick out. Grab your 3/8 Allen key and unscrew it now.
This it what it looks like straight out of the bike.
Go ahead and take out the drain plug. It helps if you disconnect the ratchet and get the socket / uni / extension bar assembly seated on the plug first. Plug the ratchet back in and undo. Just make sure the drain pan is in place before you undo the last couple of turns !!
Here's the drain plug straight out of the bike.
And wiped down.
And fitted with a new O-ring.
Have a cold beer while you wait for the oil to finish draining.
When its done get out your 7/32 Allen key and shove it up the middle of the plug... fits perfect. Use it to start the plug back into its thread and finish tightening with the socket set. You cannot tighten it with the allen key, it'll just spin inside the hole. Torque to 20 foot pounds (just gently firm with the ratchet... using about 30% hand strength).
85w - 140 high performance gear oil. An old baby's bottle makes a great oil measuring device (just make sure its spotless clean first).
Throw your funnel in the filler hole. It helps if you can jam part of the plastic funnel lip under part of your pipe's chrome heat shield. It'll hold it rock steady for you.
Fill the box with 650ml (22oz) of gear oil (it takes 2.7 fills of the baby's bottle)
In she goes.
When you're done adding the oil, screw the dipstick back in just hand tight. Sit on your bike and raise it to the upright position for 20 seconds. Throw her back on the jiffy stand and pull the dipstick back out. Add oil if necessary, a little at a time. Repeat the process until you have the right level.
Extremely easy to do, your shifting foot will love you for it.
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